diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
index 6954565..638d2eb 100644
--- a/fs/ocfs2/dlm/dlmdomain.c
+++ b/fs/ocfs2/dlm/dlmdomain.c
@@ -123,6 +123,17 @@
 LIST_HEAD(dlm_domains);
 static DECLARE_WAIT_QUEUE_HEAD(dlm_domain_events);
 
+/*
+ * The supported protocol version for DLM communication.  Running domains
+ * will have a negotiated version with the same major number and a minor
+ * number equal or smaller.  The dlm_ctxt->dlm_locking_proto field should
+ * be used to determine what a running domain is actually using.
+ */
+static const struct dlm_protocol_version dlm_protocol = {
+	.pv_major = 1,
+	.pv_minor = 0,
+};
+
 #define DLM_DOMAIN_BACKOFF_MS 200
 
 static int dlm_query_join_handler(struct o2net_msg *msg, u32 len, void *data,
@@ -133,6 +144,8 @@
 				   void **ret_data);
 static int dlm_exit_domain_handler(struct o2net_msg *msg, u32 len, void *data,
 				   void **ret_data);
+static int dlm_protocol_compare(struct dlm_protocol_version *existing,
+				struct dlm_protocol_version *request);
 
 static void dlm_unregister_domain_handlers(struct dlm_ctxt *dlm);
 
@@ -668,11 +681,45 @@
 }
 EXPORT_SYMBOL_GPL(dlm_unregister_domain);
 
+static int dlm_query_join_proto_check(char *proto_type, int node,
+				      struct dlm_protocol_version *ours,
+				      struct dlm_protocol_version *request)
+{
+	int rc;
+	struct dlm_protocol_version proto = *request;
+
+	if (!dlm_protocol_compare(ours, &proto)) {
+		mlog(0,
+		     "node %u wanted to join with %s locking protocol "
+		     "%u.%u, we respond with %u.%u\n",
+		     node, proto_type,
+		     request->pv_major,
+		     request->pv_minor,
+		     proto.pv_major, proto.pv_minor);
+		request->pv_minor = proto.pv_minor;
+		rc = 0;
+	} else {
+		mlog(ML_NOTICE,
+		     "Node %u wanted to join with %s locking "
+		     "protocol %u.%u, but we have %u.%u, disallowing\n",
+		     node, proto_type,
+		     request->pv_major,
+		     request->pv_minor,
+		     ours->pv_major,
+		     ours->pv_minor);
+		rc = 1;
+	}
+
+	return rc;
+}
+
 static int dlm_query_join_handler(struct o2net_msg *msg, u32 len, void *data,
 				  void **ret_data)
 {
 	struct dlm_query_join_request *query;
-	enum dlm_query_join_response response;
+	union dlm_query_join_response response = {
+		.packet.code = JOIN_DISALLOW,
+	};
 	struct dlm_ctxt *dlm = NULL;
 	u8 nodenum;
 
@@ -690,11 +737,11 @@
 		mlog(0, "node %u is not in our live map yet\n",
 		     query->node_idx);
 
-		response = JOIN_DISALLOW;
+		response.packet.code = JOIN_DISALLOW;
 		goto respond;
 	}
 
-	response = JOIN_OK_NO_MAP;
+	response.packet.code = JOIN_OK_NO_MAP;
 
 	spin_lock(&dlm_domain_lock);
 	dlm = __dlm_lookup_domain_full(query->domain, query->name_len);
@@ -713,7 +760,7 @@
 				mlog(0, "disallow join as node %u does not "
 				     "have node %u in its nodemap\n",
 				     query->node_idx, nodenum);
-				response = JOIN_DISALLOW;
+				response.packet.code = JOIN_DISALLOW;
 				goto unlock_respond;
 			}
 		}
@@ -733,30 +780,48 @@
 			/*If this is a brand new context and we
 			 * haven't started our join process yet, then
 			 * the other node won the race. */
-			response = JOIN_OK_NO_MAP;
+			response.packet.code = JOIN_OK_NO_MAP;
 		} else if (dlm->joining_node != DLM_LOCK_RES_OWNER_UNKNOWN) {
 			/* Disallow parallel joins. */
-			response = JOIN_DISALLOW;
+			response.packet.code = JOIN_DISALLOW;
 		} else if (dlm->reco.state & DLM_RECO_STATE_ACTIVE) {
 			mlog(0, "node %u trying to join, but recovery "
 			     "is ongoing.\n", bit);
-			response = JOIN_DISALLOW;
+			response.packet.code = JOIN_DISALLOW;
 		} else if (test_bit(bit, dlm->recovery_map)) {
 			mlog(0, "node %u trying to join, but it "
 			     "still needs recovery.\n", bit);
-			response = JOIN_DISALLOW;
+			response.packet.code = JOIN_DISALLOW;
 		} else if (test_bit(bit, dlm->domain_map)) {
 			mlog(0, "node %u trying to join, but it "
 			     "is still in the domain! needs recovery?\n",
 			     bit);
-			response = JOIN_DISALLOW;
+			response.packet.code = JOIN_DISALLOW;
 		} else {
 			/* Alright we're fully a part of this domain
 			 * so we keep some state as to who's joining
 			 * and indicate to him that needs to be fixed
 			 * up. */
-			response = JOIN_OK;
-			__dlm_set_joining_node(dlm, query->node_idx);
+
+			/* Make sure we speak compatible locking protocols.  */
+			if (dlm_query_join_proto_check("DLM", bit,
+						       &dlm->dlm_locking_proto,
+						       &query->dlm_proto)) {
+				response.packet.code =
+					JOIN_PROTOCOL_MISMATCH;
+			} else if (dlm_query_join_proto_check("fs", bit,
+							      &dlm->fs_locking_proto,
+							      &query->fs_proto)) {
+				response.packet.code =
+					JOIN_PROTOCOL_MISMATCH;
+			} else {
+				response.packet.dlm_minor =
+					query->dlm_proto.pv_minor;
+				response.packet.fs_minor =
+					query->fs_proto.pv_minor;
+				response.packet.code = JOIN_OK;
+				__dlm_set_joining_node(dlm, query->node_idx);
+			}
 		}
 
 		spin_unlock(&dlm->spinlock);
@@ -765,9 +830,9 @@
 	spin_unlock(&dlm_domain_lock);
 
 respond:
-	mlog(0, "We respond with %u\n", response);
+	mlog(0, "We respond with %u\n", response.packet.code);
 
-	return response;
+	return response.intval;
 }
 
 static int dlm_assert_joined_handler(struct o2net_msg *msg, u32 len, void *data,
@@ -899,10 +964,11 @@
 
 static int dlm_request_join(struct dlm_ctxt *dlm,
 			    int node,
-			    enum dlm_query_join_response *response)
+			    enum dlm_query_join_response_code *response)
 {
-	int status, retval;
+	int status;
 	struct dlm_query_join_request join_msg;
+	union dlm_query_join_response join_resp;
 
 	mlog(0, "querying node %d\n", node);
 
@@ -910,12 +976,15 @@
 	join_msg.node_idx = dlm->node_num;
 	join_msg.name_len = strlen(dlm->name);
 	memcpy(join_msg.domain, dlm->name, join_msg.name_len);
+	join_msg.dlm_proto = dlm->dlm_locking_proto;
+	join_msg.fs_proto = dlm->fs_locking_proto;
 
 	/* copy live node map to join message */
 	byte_copymap(join_msg.node_map, dlm->live_nodes_map, O2NM_MAX_NODES);
 
 	status = o2net_send_message(DLM_QUERY_JOIN_MSG, DLM_MOD_KEY, &join_msg,
-				    sizeof(join_msg), node, &retval);
+				    sizeof(join_msg), node,
+				    &join_resp.intval);
 	if (status < 0 && status != -ENOPROTOOPT) {
 		mlog_errno(status);
 		goto bail;
@@ -928,14 +997,41 @@
 	if (status == -ENOPROTOOPT) {
 		status = 0;
 		*response = JOIN_OK_NO_MAP;
-	} else if (retval == JOIN_DISALLOW ||
-		   retval == JOIN_OK ||
-		   retval == JOIN_OK_NO_MAP) {
-		*response = retval;
+	} else if (join_resp.packet.code == JOIN_DISALLOW ||
+		   join_resp.packet.code == JOIN_OK_NO_MAP) {
+		*response = join_resp.packet.code;
+	} else if (join_resp.packet.code == JOIN_PROTOCOL_MISMATCH) {
+		mlog(ML_NOTICE,
+		     "This node requested DLM locking protocol %u.%u and "
+		     "filesystem locking protocol %u.%u.  At least one of "
+		     "the protocol versions on node %d is not compatible, "
+		     "disconnecting\n",
+		     dlm->dlm_locking_proto.pv_major,
+		     dlm->dlm_locking_proto.pv_minor,
+		     dlm->fs_locking_proto.pv_major,
+		     dlm->fs_locking_proto.pv_minor,
+		     node);
+		status = -EPROTO;
+		*response = join_resp.packet.code;
+	} else if (join_resp.packet.code == JOIN_OK) {
+		*response = join_resp.packet.code;
+		/* Use the same locking protocol as the remote node */
+		dlm->dlm_locking_proto.pv_minor =
+			join_resp.packet.dlm_minor;
+		dlm->fs_locking_proto.pv_minor =
+			join_resp.packet.fs_minor;
+		mlog(0,
+		     "Node %d responds JOIN_OK with DLM locking protocol "
+		     "%u.%u and fs locking protocol %u.%u\n",
+		     node,
+		     dlm->dlm_locking_proto.pv_major,
+		     dlm->dlm_locking_proto.pv_minor,
+		     dlm->fs_locking_proto.pv_major,
+		     dlm->fs_locking_proto.pv_minor);
 	} else {
 		status = -EINVAL;
-		mlog(ML_ERROR, "invalid response %d from node %u\n", retval,
-		     node);
+		mlog(ML_ERROR, "invalid response %d from node %u\n",
+		     join_resp.packet.code, node);
 	}
 
 	mlog(0, "status %d, node %d response is %d\n", status, node,
@@ -1008,7 +1104,7 @@
 
 static int dlm_should_restart_join(struct dlm_ctxt *dlm,
 				   struct domain_join_ctxt *ctxt,
-				   enum dlm_query_join_response response)
+				   enum dlm_query_join_response_code response)
 {
 	int ret;
 
@@ -1034,7 +1130,7 @@
 {
 	int status = 0, tmpstat, node;
 	struct domain_join_ctxt *ctxt;
-	enum dlm_query_join_response response = JOIN_DISALLOW;
+	enum dlm_query_join_response_code response = JOIN_DISALLOW;
 
 	mlog_entry("%p", dlm);
 
@@ -1450,10 +1546,38 @@
 }
 
 /*
- * dlm_register_domain: one-time setup per "domain"
+ * Compare a requested locking protocol version against the current one.
+ *
+ * If the major numbers are different, they are incompatible.
+ * If the current minor is greater than the request, they are incompatible.
+ * If the current minor is less than or equal to the request, they are
+ * compatible, and the requester should run at the current minor version.
+ */
+static int dlm_protocol_compare(struct dlm_protocol_version *existing,
+				struct dlm_protocol_version *request)
+{
+	if (existing->pv_major != request->pv_major)
+		return 1;
+
+	if (existing->pv_minor > request->pv_minor)
+		return 1;
+
+	if (existing->pv_minor < request->pv_minor)
+		request->pv_minor = existing->pv_minor;
+
+	return 0;
+}
+
+/*
+ * dlm_register_domain: one-time setup per "domain".
+ *
+ * The filesystem passes in the requested locking version via proto.
+ * If registration was successful, proto will contain the negotiated
+ * locking protocol.
  */
 struct dlm_ctxt * dlm_register_domain(const char *domain,
-			       u32 key)
+			       u32 key,
+			       struct dlm_protocol_version *fs_proto)
 {
 	int ret;
 	struct dlm_ctxt *dlm = NULL;
@@ -1496,6 +1620,15 @@
 			goto retry;
 		}
 
+		if (dlm_protocol_compare(&dlm->fs_locking_proto, fs_proto)) {
+			mlog(ML_ERROR,
+			     "Requested locking protocol version is not "
+			     "compatible with already registered domain "
+			     "\"%s\"\n", domain);
+			ret = -EPROTO;
+			goto leave;
+		}
+
 		__dlm_get(dlm);
 		dlm->num_joins++;
 
@@ -1526,6 +1659,13 @@
 	list_add_tail(&dlm->list, &dlm_domains);
 	spin_unlock(&dlm_domain_lock);
 
+	/*
+	 * Pass the locking protocol version into the join.  If the join
+	 * succeeds, it will have the negotiated protocol set.
+	 */
+	dlm->dlm_locking_proto = dlm_protocol;
+	dlm->fs_locking_proto = *fs_proto;
+
 	ret = dlm_join_domain(dlm);
 	if (ret) {
 		mlog_errno(ret);
@@ -1533,6 +1673,9 @@
 		goto leave;
 	}
 
+	/* Tell the caller what locking protocol we negotiated */
+	*fs_proto = dlm->fs_locking_proto;
+
 	ret = 0;
 leave:
 	if (new_ctxt)